Polypropylene resins are superior in processability, water resistance, oil resistance, acid resistance and alkali resistance, but are inferior in heat resistance, rigidity, and impact resistance. Therefore, polyphenylene ether resin is blended with polypropylene resin to form a matrix of the polypropylene resin and dispersion particles of the polyphenylene ether resin, whereby a resin composition improved in heat resistance and rigidity is produced. As prior art, for example, U.S. Pat. No. 3,361,851 discloses blending polyolefin with polyphenylene ether to improve solvent resistance and impact resistance, and U.S. Pat. No. 4,383,082 and EP-A-115712 disclose blending polyphenylene ether with polyolefin and a hydrogenated block copolymer to improve impact resistance.
Furthermore, JP-A-63-113058, JP-A-63-225642, U.S. Pat. No. 4,863,997, JP-A-3-72512, JP-A-4-183748 and JP-A-5-320471 disclose addition of a specific hydrogenated block copolymer to a resin composition comprising polyolefin resin and polyphenyl ether resin to obtain a resin composition excellent in chemical resistance and processability.
Furthermore, JP-A-4-28739 and JP-A-4-28740 disclose that resin compositions excellent in balance between impact strength and rigidity are obtained by preparing resin compositions comprising polyolefin resin, polyphenylene ether resin and a specific block copolymer by a specific process.
Similarly, JP-A-7-166026 discloses that a resin composition obtained by a specific production process is excellent in impact resistance, and JP-A-7-165998 discloses that a resin composition excellent in heat resistance, impact resistance and moldability is obtained by adding a specific hydrogenated block copolymer to a resin composition comprising polyolefin resin and polyphenylene ether resin.
The applicant discloses resin compositions excellent in compatibility, rigidity, heat resistance, and solvent resistance which comprise polyphenylene ether resin, polyolefin resin and a specific hydrogenated block copolymer in JP-A-2-225563, JP-A-3-185058, JP-A-5-70679, JP-A-5-295184, JP-A-6-9828, JP-A-6-16924, JP-A-6-57130 and JP-A-6-136202.
Moreover, as for secondary battery containers, JP-A-6-203814, JP-A-8-22811 and EP-A-0691694 disclose containers comprising polyphenylene ether resin and polystyrene resin.
As seen in the above prior art, a resin composition which is a polymer alloy resin composition comprising polypropylene resin and polyphenylene ether resin and which contains the polyphenylene ether resin as dispersion particles in a matrix of the polypropylene resin is markedly improved in heat resistance and actually is considerably higher than polypropylene resin in deflection temperature under load (DTUL) which serves as an indication of heat resistance of a short period. However, at present, in the use under such environment in which internal or external pressure or load is applied for a long period of time and in addition a high temperature continues, even if improved in heat resistance indicated by deflection temperature under load (DTUL or HDT), endurance and heat resistance over a long period of time do not utterly come up with the deflection temperature under load in practical use.
Heat creep resistance is important as an indication of heat resistance under application of internal and external pressures or load over a long period of time. In the above prior art, improvement of deflection temperature under load which is heat resistance for a short time is disclosed, but they make neither mention nor suggestion of improvement of heat creep resistance.
The resin compositions of the above prior art are low in rigidity due to the effects of hydrogenated block copolymers or other elastomers used. In order to solve the problem, highly crystalline polypropylene resins are recently often used as the polypropylene resin which constitutes the matrix.
Polymer alloys of polypropylene resin-polyphenylene ether resin in which the highly crystalline polypropylene resins are used are high in heat resistance (DTUL) and superior in rigidity and heat resistance, but have practical defects such as conspicuous reduction of tenacity after thermal history, particularly, elongation and inferiority in long-term endurance as heat resistant materials.